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Fig. 6.3
Effects of TRPC channel blockers on the kisspeptin-induced inward currents at −60 mV.
(
a
) A representative recording showing that 2-APB (100
M), which had very little effect on basal
holding current, potently blocked the kisspeptin (100 nM)-evoked inward current. (
b
) Mean
I
-
V
relationship of the kisspeptin-sensitive current in the presence of 2-APB reversed at −90 mV
(
n
= 4), clearly indicating that a Kir channel was inhibited by kisspeptin. (
c
) A representative
recording showing that 2-APB (100
μ
M) applied after kisspeptin also strongly blocked the
kisspeptin-evoked inward current. (
d
) Summary of the effects of different TRPC channel blockers
(100
μ
M fl ufenamic acid) on the
kisspeptin-induced inward currents at −60 mV. Blockers were applied 5-7 min before or after the
application of kisspeptin (100 nM). The percent inhibition for the different blockers was as fol-
lows: 17.4% for 100
μ
M La
3+
, 100
μ
M 2-APB, 30
μ
M SKF96365, 250
μ
M Cd
2+
, 100
μ
μ
M La
3+
, 83.6% for 100
μ
M 2-APB, 50% for 30
μ
M SKF, 68.7% for 250
μ
M
Cd
2+
, and 89.6% for 100
M FFA. **
p
< 0.01 and ***
p
< 0.001, signifi cantly different from the
kisspeptin response under control aCSF conditions. Cell numbers tested are indicated. Error bars
indicate SEM. From Zhang C, Roepke TA, Kelly MJ, Rønnekleiv OK. Kisspeptin depolarizes
gonadotropin-releasing hormone neurons through activation of TRPC-like cationic channels.
J Neurosci 2008; 28: 4423-4434. Reprinted with permission from The Society for Neuroscience
μ
complexes of TRPC 1 + 4 or TRPC 1 + 5 subunits expressed in HEK cells with the
characteristic negative slope conductance and pronounced outward rectifi cation
(Fig.
6.2
) [
14
,
59
,
63
]. Similar current-voltage relationships have been obtained for
the leptin-induced currents in arcuate POMC and kisspeptin neurons and the
mGluR1- and CCK2-induced currents in basolateral amygdala neurons [
67
-
70
]. All
of these neurons have been found to express the same compliment of TRPC chan-
nels as GnRH neurons.
Interestingly, GnRH neurons express all of the “brain-type” TRPC channel sub-
units with the TRPC1, 4, and 5 family being the most prevalent in GnRH neurons
[
14
]. Therefore, based on the current-voltage relationship, pharmacological profi le
and mRNA expression, TRPC1, 4, and 5 are key players in mediating the excitatory
effects of kisspeptin in GnRH neurons (Figs.
6.2
and
6.3
) [
14
]. Traditionally, these
channels are known as “store operated calcium channels,” but this description is
probably the result of poorly understood signaling mechanisms [
59
,
71
]. Therefore,
current research has focused on elucidating the signaling pathway(s) by which
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